Processes for desalting crude oil under dynamic flow conditions

ABSTRACT

Presented is a process for desalting crude oil. The process includes mixing a partially dehydrated crude oil, comprising less than 10 vol. % water and at least one water-extractable contaminant, with an aqueous wash fluid. A water-in-oil emulsion is formed. The water-in-oil emulsion is introduced into a first coalescence zone defined by a first vessel. The first vessel is configured to apply an electric field to the emulsion. The water-in-oil emulsion is broken within the first coalescence zone in the presence of the electric field under dynamic flow conditions to form a partially desalted crude oil and a non-emulsified aqueous salt solution. The partially desalted crude oil and the non-emulsified aqueous salt solution are then separated from one another under the dynamic flow conditions to yield a separated, partially desalted crude oil comprising less than 1 vol. % water.

The present non-provisional application claims the benefit of pending U.S. Provisional Patent Application Ser. No. 62/060,253, filed Oct. 6, 2014, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a process for dewatering and desalting crude oil under dynamic flow conditions.

BACKGROUND OF THE INVENTION

Salts often contaminate as-produced crude oil. These salts can be admixed in the oil or they can be present in an emulsified aqueous phase such as the emulsified water of a water-in-oil emulsion. Other water-extractable contaminants are commonly present in as-produced crude oil. Sources of these salts and other contaminants found in crude oil include emulsified subterranean brines and treatment fluids used in conjunction with the production of crude oil. Inorganic salts commonly present in crude oil include salts of sodium, calcium and magnesium. Naturally present salts of organic acids, such as naphthenic acids, are also found in crude oils.

Desalting processes are typically used to reduce the salt content of crude oil feedstocks prior to refining them into higher value products. The presence of these salts in the crude oils to be processed can cause contamination of the final refined products and decrease their value. More significantly, the presence of the salts in the crude oil can cause corrosion and scaling of refinery equipment, and they can cause poisoning of the various refining catalysts. Thus, it is desirable to have efficient methods for removing the salts from crude oils to be refined.

Subterranean brines and other salt-containing fluids are frequently co-produced with crude oil usually as a component of a water-in-oil emulsion. Decreasing the initial water content of a water-in-crude oil emulsion can accomplish a significant, though typically incomplete, reduction in the salt content of a crude oil.

Various techniques for reducing the water content of emulsified water in crude oil include de-emulsification and gravitational separation of the oil and aqueous phases resulting from the de-emulsification. Other separation techniques used in dewatering crude oils containing emulsified water include the use of emulsion-breaking substances (e.g., surfactants, pH modifiers, solids removal agents, and the like) and the use of heat. These separation techniques, however, can be complicated to apply, and they can add significantly to refining costs. Moreover, these techniques often produce incomplete de-emulsification and provide for only partial salt removal from the crude oil.

Other techniques for breaking emulsions include applying an electric field or a centrifugal force to the emulsion. The application of a centrifugal force to an emulsion results in coalescence of small, emulsified water droplets until they increase sufficiently in size to form a bulk aqueous phase, also referred to herein as a continuous aqueous phase or an aqueous salt solution. The application of an electric field to an emulsion similarly promotes the coalescence of emulsified water droplets into a bulk aqueous phase.

U.S. Pat. No. 6,136,174 discloses an electrically energized compact coalescer used for breaking water-in-oil emulsions. The coalescer includes a vertical cylindrical vessel with one or more internal electrodes providing for an annulus. An emulsion is introduced into the top of the vessel and flows through the annulus wherein it is exposed to a high-intensity electrostatic field during its short residence time so that the emulsion is broken. The broken emulsion is discharged from the vessel through a bottom outlet. The coalescer device does not provide for the simultaneous application of centrifugal force with an electrical field nor does the device use the walls of its vessel to assist in the coalescence of the dispersed droplets.

U.S. Pat. No. 8,591,714 discloses an apparatus for separating water from a water-in-oil mixture. This apparatus includes a first inclined vessel that defines a confined flow path through which a water-in-oil mixture passes, and is exposed to an electrical field. The mixture then flows to a second inclined vessel having an upper oil outlet and a lower water outlet. This apparatus does not provide for the application of centrifugal force.

Though the equipment and methods disclosed in U.S. Pat. Nos. 6,136,174 and 8,591,714 can provide for breaking water-in-oil emulsions having a high initial water content, they are less effective at breaking water-in-oil emulsions having lower water levels or at providing a yielded oil product having a very low water content, especially under high flow flux rates. For example, a water-in-oil emulsion containing from 30% to 80% water by volume can be partially dewatered or dehydrated under a high flux rate of greater than 1,000 bbl/day/ft2 with the application of an electric field, but the dewatered oil typically will still have a high residual water content of from 4 to 10 vol. % and a significant salt content.

Since the prior art equipment and methods are less effective at separating water from water-in-oil mixtures having lower water levels to yield oil products having even lower concentrations of water, improved equipment and methods are needed that can provide for the effective processing of water-in-oil mixtures having low water concentrations in order to yield recovered oil products having exceptionally low water concentrations.

SUMMARY OF THE INVENTION

Accordingly, provided is a process for desalting crude oil. The process comprises providing a partially dehydrated crude oil comprising less than 10% water by volume and at least one water-extractable contaminant. An aqueous wash fluid is mixed with the partially dehydrated crude oil so as to form a water-in-oil emulsion. The water-in-oil emulsion is then introduced into a first coalescence zone defined by a first vessel. The first vessel is configured to apply a first electric field to the water-in-oil emulsion and to break the water-in-oil emulsion within the first coalescence zone under a dynamic flow condition. A partially desalted crude oil, comprising residual emulsified water of less than 1 vol. %, and a non-emulsified aqueous salt solution are yielded from the first coalescence zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a multi-stage desalting system and process of the invention.

FIG. 2 is a schematic of a vessel for use as an element of the invention configured for breaking an emulsion using an electric field.

FIG. 3 is a schematic of another vessel element of the invention configured for breaking an emulsion using a simultaneously applied centrifugal force and electric field, wherein phase separation of the emulsion components takes place within the separation zone of the vessel.

DETAILED DESCRIPTION ON THE INVENTION

The present invention is related to a process for desalting a hydrocarbon resource under dynamic flow conditions. The hydrocarbon resource comprises emulsified water, bulk water, or a combination of bulk water and emulsified water. Water-extractable contaminants, such as a salt, can also be present in the hydrocarbon resource or the water.

Conventional desalting techniques involve washing a crude oil stream after an initial water removal operation, followed by quiescent separation of an aqueous salt solution by gravitational partitioning. However, quiescent separation techniques are often slow, produce low fluxes, encompass a large vessel footprint, and result in incomplete salt removal. Such desalting techniques are also rather inefficient from a process standpoint, since their ultimate success often hinges upon successfully reducing the initial water content of the crude oil as much as possible before conducting the final washing operation to remove salt. Reducing the initial water content as much as possible frequently involves iterative processing steps and equipment, which increases operating and capital costs and provides diminishing returns. Moreover, since they involve a late-stage washing operation, conventional desalting techniques potentially “undo” the prior dewatering operations conducted on the crude oil. Further, they often require multiple stages to desalt the crude oil to a desired level.

The present inventors discovered that altering the operational order of desalting processes significantly increases process efficiency and simplicity. With the altered operational order, taking rigorous steps to lower the initial water content of an emulsion as much as possible before desalting is no longer necessary to achieve a low salt content in the separated crude oil. Moreover, the altered operational order makes high-flux processing feasible.

As used herein, the term “crude oil” refers to a mixture of hydrocarbons obtained from a geological structure, or any fraction of a mixture of hydrocarbons obtained from a geological structure. Crude oil fractions include, but are not limited to, gasoline, diesel, kerosene, fuel oil, light vacuum gas oil, heavy vacuum gas oil, as well as higher molecular weight hydrocarbon compounds.

Specifically, the inventors discovered that if the water content of an emulsified crude oil is lowered to a manageable initial level, thereby providing a manageable salt content in the crude oil, the initial dewatering operation can be conducted inexpensively and quickly. Various high-flux processing techniques for forming a partially dehydrated crude oil having a manageable water content are discussed below. The partially dehydrated crude oil is then further desalted by additional steps of the inventive process.

As used herein, the term “partially dehydrated crude oil” refers to a crude oil that has had its initial water content reduced, possibly through de-emulsification, but not completely removed to provide a decreased level of salts and other water-soluble contaminants in the crude oil. The terms “dehydrated” and “dewatered” are used equivalently in the present disclosure.

The partially dehydrated crude oil is then mixed with an aqueous wash fluid that includes water or an aqueous acid, or both. This mixing of the aqueous wash fluid with the partially dehydrated crude oil provides for emulsifying the water and formation of a water-in-oil emulsion. Then, instead of separating the aqueous wash fluid from the water-in-oil emulsion by a conventional quiescent separation method, the present inventors have discovered that by applying an electric field to the emulsion under a high flux, dynamic flow condition, a more rapid separation of the phases is promoted to yield a crude oil having a significantly reduced water and salt content below that which is provided by conventional separation methods.

As used herein, the term “dynamic flow condition” refers to a fluid that is in motion under non-quiescent conditions, such as, the movement of the fluid within a confined volume or space in a manner so as to impart or impose centrifugal force upon the moving fluid. An example of means for imparting or imposing a centrifugal force upon a fluid includes any hydrocyclone known to those skilled in the art. Acceptable hydrocyclones can have any suitable mechanical design that imparts a centrifugal force upon the introduced process fluid.

Conducting a desalting operation under dynamic flow conditions provides a number of advantages. Most significantly, dynamic flow conditions promote a more rapid separation of the crude oil, increase flux rates, and produce a lower salt content in the crude oil than is attainable through “late-stage” washing of a rigorously dewatered crude oil. Moreover, adding the aqueous wash fluid to a crude oil that still contains appreciable water does not “undo” the rigorous dewatering steps that characterize conventional desalting techniques.

Even more advantageously, the process of separating the aqueous wash fluid from the crude oil takes place in the presence of both an electric field and a centrifugal force. The inventors discovered that the electric field and the centrifugal force act synergistically with one another to promote breaking of an emulsion within a coalescence zone defined by a vessel. The synergistic combination of these features better promotes phase separation under dynamic flow conditions, thereby providing for higher process flux rates than used in alternative processes. Vessels configured and providing means for simultaneously applying an electric field and a centrifugal force to a crude oil stream are discussed in further detail below. Such vessels often have similar operational footprints to existing separator equipment, thereby allowing some measure of interchangeability within a plant setting.

In addition to the foregoing advantages, the inventive process includes removing at least a portion of the water-extractable contaminants from the crude oil. The water-extractable contaminants such as inorganic salts and oil-soluble organic salts are extracted into the aqueous wash fluid and removed from the crude oil. Other water-extractable contaminants are at least partially removed from the crude oil in a similar manner. Metal contaminants are removable as well.

Through lowering the salt and contaminant content of a crude oil by the inventive method, various refining processes are facilitated. Specifically, by lowering the salt and contaminant content of the crude oil, higher quality refined products are obtained, and a lower incidence of equipment fouling and corrosion is realized. Additionally, the more consistent feed supply provided by the high flux rates applied by the inventive desalting process better support continuous or semi-continuous refining processes.

The inventive processes will now be further described with reference to the drawings.

The flow diagram of FIG. 1 illustrates a multi-stage desalting process and system 100. In process 100, crude oil, comprising emulsified water, passes from an oil reservoir source by way of line 102 and is introduced via inlet element 104 into separation zone 106 that is defined by inclined tubular element 108. Inclined tubular element 108 houses electrode 110 that provides means for supplying an electric field within separation zone 106. Inclined tubular element 108 is further equipped with an upper outlet 112 for removing partially dehydrated crude oil from separation zone 106 and lower outlet 114 for removing bulk water from separation zone 106. Inclined tubular element 108 provides means for converting within separation zone 106 the emulsified water into bulk water and for forming partially dehydrated crude oil. The bulk water passes from separation zone 106 via lower outlet 114 and by way of line 116.

An alternative apparatus to the one described above that can be used as dehydrating means for conducting the initial dehydration of the crude oil so as to provide the partially dehydrated crude oil is the apparatus disclosed in U.S. Pat. No. 8,591,714, which patent is incorporated herein by reference. Another possible dehydrating means includes containment vessels providing residence time, which permits gravitational separation of the oil and water of the crude oil emulsion. The settling and separation can be promoted by the addition of surfactants or other emulsion-breaking chemicals.

The partially dehydrated crude oil, which comprises less than 10 vol. % water but greater than 1 vol. % water and has a concentration of a water-extractable contaminant, passes from separation zone 106 through upper outlet 112 and by way of line 120 for introduction into mixing zone 122 defined by mixer or mixing device 124. An aqueous wash fluid, comprising either water or an acid component, or both, passes by way of line 130 and is introduced into mixing zone 122. Mixer 124 provides means for mixing the partially dehydrated crude oil and aqueous wash fluid to form or yield a water-in-oil emulsion.

The water-in-oil emulsion is conveyed via line 134 and introduced into first coalescence zone 136 that is defined by first vessel 140. First vessel 140 is operatively configured with first electrode 142 providing means for supplying a first electric field within first coalescence zone 136 and for supplying or applying the first electric field to the water-in-oil emulsion. The first electric field contributes to the breaking of the water-in-oil emulsion within first coalescence zone 136.

First vessel 140 is further configured to provide means for inducing a dynamic flow condition within first coalescence zone 136. This can be achieved by the configuration or design of first vessel 140 so that it induces or applies centrifugal force 144 to the water-in-oil emulsion within first coalescence zone 136. One way of providing for the application of centrifugal force 144 is for first vessel 140 to provide the function of a hydrocyclone.

By applying the electric field and the dynamic flow condition created by the centrifugal force to the water-in-oil emulsion, it is more efficiently broken than when either the electrical field or the centrifugal force is alone applied. The dynamic flow condition in combination with the application of the electrical field provide for good separation of the components of the water-in-oil emulsion under high flux rates.

Thus, first vessel 140 provides means for breaking the water-in-oil emulsion so as to provide a continuous phase of a partially desalted crude oil that comprises residual emulsified water of less than 1 vol. % but typically greater than 0.3 vol. % of the partially desalted crude oil and a continuous phase of a non-emulsified aqueous salt solution. The partially desalted crude oil is yielded and passes from first coalescence zone 136 by way of line 148, and the non-emulsified aqueous salt solution is yielded and passes from first coalescence zone 136 through line 158.

The partially desalted crude oil is introduced by way of line 148 into second coalescence zone 160 that is defined by second vessel 162. Second vessel 162 is operatively configured with second electrode 164 providing means for supplying a second electric field to the partially desalted crude oil and means for applying second centrifugal force 166 to the partially desalted crude oil. One means for inducing second centrifugal force 166 and applying it to the partially desalted crude oil is by the use of a hydrocyclone.

The simultaneous application of the second electric field and second centrifugal force 166 within second coalescence zone 160 contributes to the conversion of the residual emulsified water contained in the partially desalted crude oil into the continuous phase of a further portion of non-emulsified aqueous salt solution. Thus, second vessel 162 provides means for removing the residual emulsified water of the partially desalted crude oil by coalescing the water particles of the residual emulsified water into a bulk continuous phase and yielding a further portion of non-emulsified aqueous salt solution and a desalted crude oil.

The desalted crude oil is removed from second coalescence zone 160 and passes downstream as a feedstock for a refinery crude unit or other processing unit (not shown) through line 170. The further portion of non-emulsified aqueous salt solution is removed and passes from second coalescence zone 160 by way of line 172.

Any one or more streams of bulk water passing through line 116, or the non-emulsified aqueous salt solution passing through line 158, or the further portion of non-emulsified aqueous salt solution passing through line 172 may be recycled to mixer 124 for mixing with the partially dehydrated crude oil, provided, that their purity is sufficient to provide for the removal of water-extractable contaminants from the partially dehydrated crude oil.

The inventive process provides for the separation and removal of water and salt components from a partially dehydrated crude oil that comprises an unacceptably high concentration of water but less than 10 vol. % water and at least one water-extractable contaminant.

The water content of the partially dehydrated crude oil can vary over a wide range, which may be dictated, at least in part, by the technique through which the initial water removal is carried out on an emulsified crude oil feed. Conventional high-flux dewatering techniques readily provide for a water content below 10 vol. % but greater than 1 vol. %. Typically, however, the water content of the partially dehydrated crude oil is in the range of from 2 vol. % to 9 vol. % water range. More typically, the water content of the partially dehydrated crude oil is greater than 3 vol. % and less than 8 vol. %.

The crude oil feedstock that undergoes or is charged to an initial dehydration stage or step contains a large amount of a water that is in the form of a non-continuous water phase or emulsified water within the continuous oil phase of the crude oil feedstock. Typically, the amount of water in this crude oil feedstock is greater than 12 vol. % of the total crude oil feedstock and can be in the range of upwardly to 80 vol. % or 90 vol. % of the total crude oil feedstock (i.e., oil plus water and other components). Typical water levels in the crude oil feedstock of the invention can be in the range of from 15 vol. % to 75 vol. %, and, more typically, they are in the range of from 20 vol. % to 70 vol. %.

The one or more water-extractable contaminants in the partially dehydrated crude oil include inorganic salts that are removable by the inventive process. Such inorganic salts include those selected from the group of inorganic salt compounds consisting of sodium chloride, sodium bromide, potassium chloride, potassium bromide, calcium chloride, and magnesium chloride. These inorganic salts commonly occur in a subterranean environment and are used in various subterranean treatment operations. Organic salts, such as formate salts from formate brines, and naphthenic acid salts, can also be present in the partially dehydrated crude oil and are also removable by the inventive process.

Other water-extractable contaminants are also removable from a partially dehydrated crude oil by the inventive processes. Examples of other water-extractable contaminants that are removable in an aqueous salt solution include surfactants, water-soluble polymers, surfactant-polymer blends, alkaline-surfactant-polymer blends, metals and metal oxides such as iron or iron oxide, iron sulfates, amines and trampamines, asphaltenes, waxes, resins, solids (e.g., clay particles, sand particles, bitumen, catalyst fines, bacteria and other microorganisms, and the like), silicon oxides, quartz and the like. While all of these contaminants are not necessarily water-soluble, they can all be made at least water-extractable by using a wettability altering agent or an interfacially active agent.

In the mixing step of the inventive process, an aqueous wash fluid, comprising water, is mixed with the partially dehydrated crude oil under conditions for forming a water-in-oil emulsion. The amount of water mixed with the partially dehydrated crude oil is such as to provide a water content of the water-in-oil emulsion that is in the range of from 2 vol. % to 15 vol. % of the volume of water-in-oil. The preferred level of water in the water-in-oil emulsion is in the range of from 4 vol. % to 15 vol. %, and, more preferred, it is in the range of from 5 vol. % to 8 vol. % water. A water content of less than 2 vol. % is believed to provide insufficient capacity for removal of water-soluble contaminants from the crude oil. A water content higher than 15 vol. % is believed to present a waste disposal issue.

The amount of aqueous wash fluid mixed with the partially dehydrated crude oil is controlled in order to produce a particular water content within the water-in-oil emulsion so as to achieve a desired degree of contaminant removal while keeping the total volume of the water-in-oil at a manageable level for processing. The amount of aqueous wash fluid mixed with the partially dehydrated crude oil is kept to a minimum level in order to minimize waste disposal or remediation costs of the spent wash fluid following de-emulsification.

The partially desalted crude oil has a significantly reduced water content over that of the water-in-oil emulsion charged to the first coalescence zone in which the water-in-oil emulsion is broken. In the first coalescence step, the reduction or lowering of the water content of the water-in-oil emulsion provides for a significant decrease in the level of salts and other water-extractable contaminants contained in the partially dehydrated crude oil. It is desirable to achieve this reduction in salt and water content of the crude oil in the downstream refining processes. The final water content of the crude oil determines, at least in part, the extent to which desalting and mitigation of other water-extractable contaminants in the crude oil occurs.

The partially desalted crude oil that is yielded from the first coalescence zone of the process typically will contain greater than 0.3 vol. % water but less than 1 vol. %. More typically, however, this process step provides a partially desalted crude oil having less than 0.8 vol. % water, or less than 0.7 vol. % water, or less than 0.5 vol. %. Thus, the partially desalted crude oil typically will contain water in the range of from 0.3 vol. % to 1 vol. %. More typically, the water content is greater than 0.3 vol. % upwardly to less than 0.8 vol. % water, or less than 0.7 vol. % water, or less than 0.5 vol. %.

The second coalescence step provides for an exceptionally low concentration level of water in the finally yielded desalted crude oil which makes it especially suitable for processing as a feed stock to a refinery unit. The desalted crude oil that is yielded from the second vessel of the process typically will contains less than 0.3 vol. % water. It is preferred, however, for the water content of the desalted crude oil to be less than 0.1 vol. %, and, more preferred, it is less than 0.01 vol. %. A practical lower limit for the water content is greater than 10 ppmv or greater than 100 ppmv.

FIG. 2 is a schematic of vessel 200 that can suitably be used in place of the inclined tubular element 108 of FIG. 1 with its inlet element 104. Vessel 200 provides means for breaking an emulsion using an electric field and includes elongated inlet element 210 which houses electrode 220. Elongated inlet element 210 is inclined with respect to the earth's surface and forms a fluid connection for flowing or feeding fluid into separation zone 232 defined by inclined tubular element 230. Crude oil is introduced into elongated inlet element 210 wherein it is exposed to the electric field established by electrode 220. Elongated tubular element 230 includes upper outlet 240 providing for the removal of partially dehydrated crude oil from separation zone 232 and lower outlet 250 providing for the removal of bulk water from separation zone 232.

After the initial crude oil emulsion breaks in the presence of an electric field within elongated inlet element 210, further separation take places within separation zone 232 to yield a partially dehydrated crude oil and a bulk water or aqueous phase. In this separation, the more dense bulk aqueous phase settles to the bottom of inclined tubular element 230 and is removed through lower outlet 250 and the less dense partially dehydrated crude oil component rises within inclined tubular element 230 and is removed through upper outlet 240. Partially dehydrated crude oil removed through upper outlet 240 is then passed downstream for further treating. Further operational details of vessel 200 may be obtained from U.S. Pat. No. 8,591,714.

The equipment described in U.S. Pat. No. 8,591,714 and depicted in summary form in FIG. 2 can also be used as one or more of the elements of the inventive process by providing means for separating components of a process fluid or means for desalting a process fluid. This equipment further can include modifications as described herein.

In addition to providing for the separation of bulk water from crude oil, this apparatus can also provide for the breaking of water-in-crude oil emulsions, resulting in at least a partial desalting of the crude oil to yield a partially desalted crude oil and a non-emulsified aqueous salt solution. This equipment can further be modified to provide for separating partially desalted crude oil and non-emulsified aqueous salt solution from one another under a dynamic flow condition.

When using the apparatus of U.S. Pat. No. 8,591,714 as the first vessel component of the inventive process, the water-in-oil emulsion formed from the partially dehydrated crude oil is introduced into an inlet element that houses an electrode, wherein the water-in-oil emulsion experiences or is exposed to an electric field. The emulsion breaks in the presence of the electric field, and the broken emulsion passes into a separation zone from which a partially desalted crude oil is removed through an upper outlet and a non-emulsified aqueous salt solution is removed through a lower outlet.

Vessel 200 can also be modified to provide a centrifugal force within elongated inlet element 210 such that the centrifugal force and electric field are simultaneously applied to a fluid stream. For example, a feed to elongated inlet element 210 is introduced tangentially thereby inducing rotational motion and an accompanying centrifugal force to the fluid stream. Accordingly, vessel 200 can be configured as a hydrocyclone in order to produce the rotational motion and centrifugal force.

Other vessels that suitably provide means for simultaneously applying a centrifugal force and an electric field to a water-in-oil emulsion formed from partially dehydrated crude oil are described in commonly owned U.S. patent application Ser. Nos. ______ and ______, each entitled “Systems and Processes for Separating Emulsified Water from a Fluid Stream,” filed concurrently herewith, and each of which is incorporated herein by reference in its entirety.

FIG. 3 is a schematic of hydrocyclone 300 that can suitably be used in place of either first vessel 140 or second vessel 162, or in place of both these vessels, of FIG. 1. Hydrocyclone 300 is configured to provide means for simultaneously conveying an electric field and a centrifugal force to a process fluid stream, such as a water-in-oil emulsion stream or a partially desalted crude oil stream, or both. Hydrocyclone 300 defines coalescence zone 302 wherein separation of the emulsion components occurs.

Fluid inlet 310 is tangentially connected to vessel 312 of hydrocyclone 300 such that a centrifugal force is conveyed to an introduced fluid stream. Separation of the water from the oil of a water-in-oil emulsion takes place within coalescence zone 302, and a light emulsion component is removed through fluid outlet 320 and a heavy emulsion component is removed through outlet 330. For example, when used in the inventive process, desalted crude oil is removed through fluid outlet 320 and an aqueous salt solution is removed through fluid outlet 330. Differential separation takes place by virtue of the higher density of water and its greater mobility toward the outer walls of hydrocyclone 300.

Hydrocyclone 300 is also configured to convey an electric field within coalescence zone 302. Electrode 340 is disposed within hydrocyclone 300 in order to convey an electric field. Although electrode 340 is depicted as being coincident with longitudinal axis 350, other configurations are possible. For example, electrode 340 can be parallel to longitudinal axis 350 while it is axially offset within hydrocyclone 300. Preferably, electrode 340 makes an oblique angle with respect to longitudinal axis 350 such that it is non-parallel to longitudinal axis 350.

When inclined with respect to the earth's surface, electrode 340 makes an incident angle with the earth's surface in the range of from 20 degrees to 60 degrees, wherein the incident angle is measured as the angle of inclination between electrode 340 and a plane parallel to the earth's surface. More preferably, electrode 340 is oriented at an incident angle in the range of from 22 degrees to 45 degrees.

Hydrocyclone 300 also can be inclined with respect to the earth's surface. In this embodiment, longitudinal axis 350 makes an incident angle with the earth's surface in the range of from 20 degrees to 60 degrees and, preferably, from 22 degrees to 45 degrees. Electrode 340 can additionally be coincident with longitudinal axis 350, or it can be oriented at an oblique angle to longitudinal axis 350.

Regardless of whether hydrocyclone 300 or electrode 340, or both, are inclined with respect to the earth's surface when used in breaking an emulsion, advantageous features are realized by utilizing these orientations. By providing an inclined surface within hydrocyclone 300, emulsified water droplets more readily interact with the inclined surface and coalesce into an aqueous salt solution due to their easier surface access; because, the inclination provides for a shorter settling distance of the water droplets before they strike the inside wall of the inclined vessel. Similar benefits are realized by disposing electrode 340 at an oblique angle.

The exterior of electrode 340 can be insulated so that it applies an electric field to the emulsified fluid stream without directly applying a current to it. Electrode 340 can also have a substantially linear geometry, and it can be either solid or tubular.

The insulation of electrode 340 is any suitable dielectric coating material, including polymers that are typically used for providing electrical insulation. Preferred insulation includes a dielectric coating material.

The electric field applied in the inventive process can vary in magnitude over a wide range, and the magnitude of the applied field can be varied to achieve a desired degree of coalescence of emulsified water droplets. The applied voltage producing the electric field can range from 500 volts to 40,000 volts, and, more preferably, it can range from 15,000 volts to 20,000 volts. The electric field is applied with either an alternating current or a direct current.

The electric field is applied either continuously or it is pulsed. When pulsed, the pulse rate is in a range from 0.1 Hz to 50 Hz, or from 0.1 Hz to 10 Hz, or from 1 Hz to 5 Hz. Waveforms other than pulsing the applied voltage can be used.

The water droplets or particles of the water-in-oil emulsion or partially desalted crude oil are of a size in the range of from 10 nm to 100 microns. More typically, however, the water particles have a size in a range of from 25 nm to 10 microns, and, most typically, from 50 nm to 1 micron. Any combination or subrange of these droplet sizes may be present in the water-in-oil emulsion. Water droplet sizes above 100 microns in diameter are considered to be a bulk aqueous phase for purposes of the present disclosure.

The rate at which the emulsified fluid stream (i.e., water-in-oil emulsion or partially desalted crude oil) is introduced into the coalescence zone(s) of the process is such as to provide a flux rate of at least 1,000 bbl/day/ft2 (bbl=barrel=42 US gallons) while still providing partially desalted crude oil or desalted crude oil having a reduced water content in the concentration ranges described in detail elsewhere in this specification. The value used for the cross-sectional area term (ft2) of the flux formula is the effective cross-sectional area of the vessel (i.e., of the plane area that is perpendicular to the vertical axis of the vessel defining the coalescence zone) into which the emulsified fluid stream is introduced.

While it is important to the invention for the flux rate reference above to be at least 1,000 bbl/day/ft2, it is preferable for it to be as high as is feasible while still providing for the necessary reduction in water content of the desalted crude oils. Thus, the flux rate preferably can be at least 1,500 bbl/day/ft2 or at least 2,000 bbl/day/ft2. Due to technical and practical limits of the inventive process, there is a practical upper limit to the flux rate. Therefore, the flux rate can be in the range from 1,000 bbl/day/ft2 to 6,000 bbl/day/ft2, or from 1,500 bbl/day/ft2 to 5,000 bbl/day/ft2, or from 2,000 bbl/day/ft2 to 4,500 bbl/day/ft2, or from 2,500 bbl/day/ft2 to 4,000 bbl/day/ft2, or from 4,000 bbl/day/ft2 to 5,000 bbl/day/ft2. 

1. A process, comprising: providing a partially dehydrated crude oil that comprises less than 10 vol. % water and a water-extractable contaminant; mixing an aqueous wash fluid with the partially dehydrated crude oil and forming a water-in-oil emulsion; introducing the water-in-oil emulsion into a first coalescence zone defined by a first vessel, wherein the first vessel is configured to apply a first electric field to the water-in-oil emulsion and to break the water-in-oil emulsion within the first coalescence zone in the presence of the first electric field and under a dynamic flow condition; and yielding from the first coalescence zone a partially desalted crude oil, comprising residual emulsified water of less than 1 vol. % water, and a non-emulsified aqueous salt solution.
 2. The process of claim 1, wherein the process further comprises: introducing the partially desalted crude oil into a second coalescence zone defined by a second vessel configured to simultaneously apply a second centrifugal force and a second electric field to the partially desalted crude oil to convert the residual emulsified water into a further portion of non-emulsified aqueous salt solution; and removing from the second coalescence zone a desalted crude oil and the further portion of non-emulsified aqueous salt solution.
 3. The process of claim 2, wherein the second vessel is a second hydrocyclone having a second longitudinal axis and including a second electrode placed within the second coalescence zone in a non-parallel orientation with respect to the longitudinal axis.
 4. The process of claim 3, wherein the second hydrocyclone is inclined with respect to the earth's surface at a second incident angle in the range of from 20 degrees to 60 degrees.
 5. The process of claim 4, wherein the non-emulsified aqueous salt solution comprises the water-extractable contaminant.
 6. The process of claim 5, wherein the aqueous wash fluid comprises water or an aqueous acid solution.
 7. The process of claim 6, wherein the step of providing the partially dehydrated crude oil comprises: passing a crude oil, comprising emulsified water, through an inlet element into a separation zone defined by an inclined tubular element housing an electrode and having an upper outlet and a lower outlet, wherein the inclined tubular element provides for converting the emulsified water into bulk water and for forming the partially dehydrated crude oil; and removing from the separation zone the partially dehydrated crude oil through the upper outlet and the bulk water through the lower outlet.
 8. The process of claim 7, wherein the first vessel is further configured to simultaneously apply a first centrifugal force to the water-in-oil emulsion while applying the first electric field.
 9. The process of claim 8, wherein the first vessel is a first hydrocyclone having a first longitudinal axis and includes a first electrode placed within the first coalescence zone in a non-parallel orientation with respect to the first longitudinal axis.
 10. The process of claim 9, wherein the first hydrocyclone is inclined with respect to the earth's surface at an first incident angle in the range of from 20 degrees to 60 degrees.
 11. The process of claim 10, further comprising: adding a chemical to the partially dehydrated crude oil or the water-in-oil emulsion, or both, to further promote coalescence of emulsified water into the non-emulsified aqueous salt solution.
 12. The process of claim 11, further comprising: refining the desalted crude oil. 